Delirium is the second most common psychiatric diagnosis among hospitalized elderly cancer patients. A variety of factors are known to cause delirium in cancer patients, and the most frequently observed are outlined. History, presence of an altered mental state with identification of the cognitive impairment, and a close watch of mental function will help to differentiate delirium from a normal stress reaction, an adjustment disorder to cancer diagnosis, or early dementia. As in other medically ill patients, antipsychotic drugs are the cornerstone of treatment for delirium not manageable with environmental manipulation or causal therapy. Haloperidol is the most commonly prescribed drug for delirium in the cancer setting because of its low cardiovascular and anticholinergic effects. Cancer patients who are debilitated require a much lower starting dose than do the physically healthy.